Pre-heat oven to 350°F and line 2 baking sheets with parchment paper or a silicone mat.

In a large bowl, whisk together the flour, baking powder, baking soda, and salt to combine. Set aside. In a small bowl, whisk together the buttermilk and vanilla to combine. Set aside.

In the bowl of a stand mixer fitted with the paddle attachment, beat the shortening and sugars on medium speed until fluffy, scraping down the sides as necessary.

Reduce the speed to medium-low and add in the eggs one at a time, mixing just until combined before adding the next.

Scrape down the sides and slowly pour in the buttermilk mixture. Reduce the mixer to low and add the flour mixture in three additions. Scrape down the sides and mix for a few seconds longer just until a few streaks of flour remains.

Drop 2 tablespoonfuls of dough onto the prepared baking sheets, spacing 2-inches apart. Bake for 9 to 11 minutes, just until the edges are golden brown. Cool on the baking sheet for 10 minutes before transferring to a cooling rack to cool completely. Repeat with the remaining dough.

To make the glaze, melt the butter and brown sugar in a small saucepan over low heat, stirring constantly. Once melted, stir in the salt and milk. Remove from heat and add in the powdered sugar, about 2 tablespoons at a time until a spreadable consistency is achieved. Let sit to cool until thickened. Decorate cooled cookies as desired.